1. Field of the invention
This invention relates to a time division digital switching system for circuit mode and packet mode channels having a predetermined bit-rate. The channels convey useful information words having a predetermined number of bits, such as data words or voice sample words.
More particularly, the system comprises G first multiplexing means each of which multiplexes a group of I reception channels into an outgoing multiplexed signal, G first demultiplexing means, each of which demultiplexes an incoming multiplexed signal into a group of I emission channels wherein each multiplexed signal has a recurrent frame comprising I useful information words assigned to the multiplexed channels, and means for bidirectionally switching the circuit mode channels and the packet mode channels between the incoming and outgoing multiplexed signals.
2. Description of the Prior Art
Such a system, also referred to as a multiservice switching system, is described in European patent application No. 34,514 (which corresponds to the U.S. patent application Ser. No. 231,936, filed Feb. 4, 1981). The reception channels are delivered by subscriber lines having a circuit mode channel for voice and a packet mode channel for data and by circuit mode or packet mode monochannel lines via individual equipments.
An individual equipment of a subscriber line comprises second multiplexing means for demultiplexing the channels. An individual equipment for a subscriber line or a monochannel packet mode line comprises a detector which detects flag/packet transitions in the packet mode channel. This detector transmits the address of the channel to the marking unit in the switching network or means of the multiservice system responsive to the detection of such a transition, via a specialized link. Likewise, when the packet switching unit associated with the multiservice system has a packet to transmit, it sends the address of the free packet mode monochannel line selected to the marking unit, again via a specialized link.
Organizing the system in such a fashion requires, on the one hand, that the individual equipments be in the vicinity of the switching network and, on the other hand, wiring that is both laborious and far from accessible from inside the switching network via specialized links when new packet mode individual equipment is connected.
Furthermore, the foregoing multiservice system does not allow subscriber lines having more than two multiplexed channels to be connected. Such lines are already known for example in French patent application No. 2,412,994 which deals with a multiservice system based on a packet mode switching network which is separated from a circuit mode switching network. The demand for lines permitting the simultaneous transmission of several voice channels and several packet channels is ever present with the growing needs of telematic subscribers.